This invention relates to an ignitor for an internal combustion engine.
FIG. 3 is an exploded perspective view of a known ignitor for an internal combustion engine. The ignitor comprises an ignition coil 1 disposed within an interior space or a coil mounting portion 11 of a casing 10. The ignition coil 1 comprises an iron core 2 disposed partially in the mounting portion 11 of the casing 10, a primary winding 4 wound around the iron core 2 within the casing 10 and a secondary winding 5 wound on the outer circumference of the primary winding 4.
A resin-molded power-transistor package 6 is disposed within the casing 10. The power-transistor package 6 is supported by means of a holder 8 which is inserted into the casing 10 along a pair of guides 13 disposed to two of internal surfaces of the side walls of the casing 10. The power-transistor package 6 is composed of a power transistor (not shown), the current limiting circuit (not shown), etc. which are mounted on a lead frame (not shown) having a plurality of leads 15 and are hermetically sealed with a suitable resin. The power-transistor package 6 is covered with cover means such as a silicone sheet 7.
The casing 10 also integrally comprises an electrical connector 12 which has integrally formed therein a plurality of connector terminals 12a electrically connected to the ignition coil 1 and terminals 6a of the power-transistor package 6 through holder terminals 8a of the holder 8 and a separate conductor (not shown). One of the terminal 6a of the power-transistor package 6 is also electrically connected to the ignition coil 1 through the holder terminal 8a of the holder 8. Disposed to the bottom of the casing 10 is a secondary terminal 14 for supplying a high voltage generated in the secondary winding 5 of the ignition coil 1 to the ignition plug (not shown) through the distributor (not shown) to ignite the internal combustion engine (not shown).
An insulating resinous filler material (not shown) is filled within the interior space of the casing 10 for unifying and protecting the ignition coil 1 and the power-transistor package 6. The insulating resinous filler material and the power-transistor package 6 have different coefficients of thermal expansion each other, however, the silicone sheet 7 which covers the power-transistor package 6 absorbs a stress caused by the difference between these coefficients of thermal expansion thereof resulting from repeated violent changes of temperature of the surroundings thereof.
In the known ignitor as above described, when the power transistor of the power-transistor package 6 turns off to interrupt a primary current flowing through the primary winding 4 of the ignition coil 1 in accordance with an ignition timing of the internal combustion engine (not shown), a high voltage generates on the secondary winding 5 of the ignition coil 1 and is supplied to the distributor (not shown) through the secondary terminal 14 to ignite the internal combustion engine (not shown).
In the manufacture of the known ignitor as described above, firstly, the primary winding 4 is disposed within the mounting portion 11 of the casing 10 and the secondary winding 5 is disposed around the primary winding 4. Next, the power-transistor package 6 is covered with the silicone sheet 7 and mounted on the holder 8 so that the terminals 6a of the power-transistor package 6 is electrically connected to the holder terminals 8a of the holder 8. Thus, the power-transistor package 6 with the silicone sheet 7 thereon and the holder 8 constitute a power-transistor package assembly. The power-transistor package 6 is mounted to the mounting portion 11 of the casing 10 together with the silicone sheet 7 and the holder 8 along the pair of guides 13 disposed to the internal surfaces of the casing 10 opposite to each other. Then, the primary and secondary windings 4 and 5 of the ignition coil 1, the holder terminals 8a of the holder 8, the terminals 12a of the connector 12 and the secondary terminal 14 are electrically connected to the respective components. Further, the iron core 2 is inserted into the primary coil 4 and the insulating resinous filler material (not shown) is poured into the interior space of the casing 10 and cured to unify and seal the ignition coil 1 and the power-transistor package 6 within the casing 10.
In the known ignitor, as described above, after the primary and secondary windings 4 and 5 of the ignition coil 1 and the power-transistor package 6 with the holder 8 (power transistor package assembly) is mounted within the mounting portion 11 of the casing 10, electrical connections must be provided between the terminals 12a of the connector 12 and the ignition coil 1 within the limited space in the casing 10. Some of the electrical connections may be provided through direct connections between terminals but some other electrical connections such as the connections between the connector terminal 12a and the ignition coil 1 must be provided through separate electrical conductors. These connecting portions sometimes fail to be tightly and correctly connected and it may be easily damaged.
Further, since the connector 12 is integrally formed in the casing 10, the shape and the mounting direction of the connector 12 are difficult to change and, therefore, the known ignitor has a poor versatility in the industry.